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Old November 24th 18, 03:22 PM posted to
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Default Adjusting SDRs for better fidelity on shortwave

From the Apache Labs email reflector:

On 11/24/2018 9:39 AM, Scott Traurig
[apache-labs] wrote:
More to your points, I am an unabashed fan of NR2. For me it works
extremely well in both performance categories, both inter-syllabic
noise suppression and in improving intelligibility with low SNR
speech. Because of its former properties I tend to leave it turned
on all the time, even on high SNR signals, and for listening to CW
as well. I am so noise averse that I am also an unabashed fan of the
quite wonderful syllabic squelch algorithm in PowerSDR (which came
over from the Flex legacy version, I think), and will use that for
QSOs with medium to high SNR signals in concert with NR2. When
listening with both NR2 and squelch turned on, to signals with a
wider than average passband, say 50Hz to 3.5KHz, I find the
experience quite FM-like [...]

Interesting discussion. I enjoy an FM-like experience, too. But I
dislike the artificiality of squelch or of even the best NR
algorithms (and our NR2 is the best), which to my ear add so many
artifacts that they make the station I'm listening to sound like a
low-bitrate mp3 from 1998 -- totally intolerable.

I'll use it in the rare cases when nothing else lets me copy a
marginal signal. But for the most part, I'd rather hear a bit of
noise than hear grungy artifacts. In fact, I think the artifacts
from NR (like those in a low-bitrate compressed file) hinder my
brain from listening _deep into the noise_ and picking out subtleties.

NR has come a long way. But so far, in my view, nothing beats the
algorithms in our brains.

Here's how I try to approach an FM-like experience: Adjusting the
AGC gain so that the background noise is 20 or so dB below the peaks
of a loud signal on an output level meter (the one in Audacity or
the free Orban meter works fine) helps a _lot_, as does _slowing
down_ the AGC to as slow as it will go in PowerSDR (5000 ms). (When
you have it that slow, you can just turn off the hang feature, which
isn't needed, which makes the gradual gain increase sound very
natural and barely noticeable.) And, no, I don't have any problem
hearing weak signals after the cessation of a strong one. The
ear/brain combo does just fine with the brief drop in level.

Doing those two things _greatly_ improves perceived fidelity and
reduces listener fatigue.


Kevin, WB4AIO.

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